Expand window scale factors up to 8×

5× is just about the highest factor useful for a 3840×2160 (“4K”)
monitor with games running in 320×200 mode.  7680×4320 (“8K”) monitors
are also on the market and the higher scale factors should be useful
for them too.

src/qt/languages/en-US.po

@@ -76,6 +76,24 @@ msgstr "1.&5x"
 msgid "&2x"
 msgstr "&2x"
 
+msgid "&3x"
+msgstr "&3x"
+
+msgid "&4x"
+msgstr "&4x"
+
+msgid "&5x"
+msgstr "&5x"
+
+msgid "&6x"
+msgstr "&6x"
+
+msgid "&7x"
+msgstr "&7x"
+
+msgid "&8x"
+msgstr "&8x"
+
 msgid "Filter method"
 msgstr "Filter method"